Lenz's Cooking Foil

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Science on Stage 2019, Cascais, Portugal 94 Electricity & Magnetism Lenz’s Cooking Foil (Ireland) Background: Follow these steps: opposite to the polarity of the falling magnet and there is a The Russian physicist 1. Hold the aluminium tube force of repulsion according Heinrich Friedrich Emil Lenz so that it is vertical to the Lorentz Force. This 1804-1865 formulated the 2. Drop the non-magnetic force is not strong enough to law that states that the di- object into the tube stop the falling magnet, but it rection of an induced current 3. Note the time it takes to is large enough to noticeably in a conductor opposes the fall through slow it down. change causing it. 4. Repeat with the neodymi- Many teachers may be What next? um magnet noting the time familiar with experiments that • Investigate the effect when it takes to fall through demonstrate this law. A pop- using different strengths ular one involves dropping a 5. Compare the two times and sizes of magnets and strong magnet into a hollow tubes. tube, made from a non-mag- So what happened? • Challenge students to ex- netic metal such as copper plore applications that use or aluminium. There can be As the magnet falls it induces Lenz’s law such as: metal difficulties sourcing suitable an electrical current in the detectors, braking systems tubes and magnets. Kits can tube. This current has a on trains, induction motors be bought from suppliers but magnetic field. According etc . can be expensive. to Lenz’s law, the polarity is This low cost variation uses common kitchen cooking foil and works very well. You will need: 9 A strong neodymium magnet 9 A small non-magnetic object 9 Some aluminium cooking foil tubes (ideally different heights) 9 A timer such as on a smart phone Image credit: lockhaven.edu.

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